Ok,
I'm a bit stuck here with this one - it's a bit nasty.
I've let the bootsector decrypt itself and let it load the first 6 tracks to $17d22.  Easy peasy bit
That data is then relocated (also is partially decrypted) down to $200.  I've got that block saved as a 38k file for future use.
All system is trashed here (Toxic Monst does help though)
Code runs at $200, all traps, vbl, trace / kbd vector / timers are then screwed around with and custom ones setup as more sectors are loaded.
If you manage to get past that and still have a working system then please let me know.
I would ideally like to find where the sector loader is kept.
I did manage to load more tracks but then the system got trashed again from somewhere else.
I've unpacked Andy Arfling (Au121) 1 meg file crack and can't work out what he did with it to stop it loading sectors.!  :-[